This invention relates to a fuel supply control method for internal combustion engines, and more particularly to a method of this kind which is adapted to control the quantity of fuel being supplied to the engine at the start of the engine to ensure smooth starting of the engine when an abnormality or failure occurs in the engine temperature detecting means.
A fuel supply control system adapted for use with an internal combustion engine, particularly a gasoline engine has been proposed e.g. by U.S. Pat. No. 3,483,851, which is adapted to determine the valve opening period of a fuel quantity metering or adjusting means for control of the fuel injection quantity, i.e. the air/fuel ratio of an air/fuel mixture being supplied to the engine, by first determining a basic value of the above valve opening period as a function of engine rpm and intake pipe absolute pressure and then adding to and/or multiplying same by constants and/or coefficients being functions of engine rpm, intake pipe absolute pressure, engine temperature, throttle valve opening, exhaust gas ingredient concentration (oxygen concentration), etc., by electronic computing means.
According to this proposed system, as the quantity of fuel being supplied to the engine at the start of the engine is determined to a very large extent in dependence upon the engine temperature (e.g. engine cooling water temperature), the value of an engine cooling water temperature-dependent coefficient is set such that the lower the engine cooling water temperature, the larger the quantity of fuel being supplied to the engine is set to, so as to obtain smooth starting of the engine. However, if an abnormality occurs in the function of the sensor means for detecting engine cooling water temperature, the value of the engine cooling water temperature-dependent coefficient is not set to a proper value so that it becomes very difficult to achieve smooth starting of the engine as the quantity of fuel supplied to the engine is not adapted to the engine cooling water temperature.
Even when the engine comes into a post-starting operating condition where the cranking rpm of the engine is exceeded to start normal fuel supply control, if the fuel quantity is not corrected by the engine cooling water temperature-dependent correction coefficient in the event of occurrence of an abnormality in the function of the water temperature sensor means, the fuel quantity cannot be controlled to a proper value with accuracy, resulting in stoppage of the engine or degradation in the emission characteristics and driveability of the engine.